1. Field of the Invention
Aspects of the present invention relate to a thin film transistor (TFT), a method of fabricating the TFT, an organic light emitting diode (OLED) display device having the TFT, and a method of fabricating the OLED display device. More particularly, aspects of the present invention relate to a TFT in which an amount of a crystallization-inducing metal remaining in a channel region of a semiconducting layer crystallized using the crystallization-inducing metal is reduced by gettering to improve the electrical properties of the TFT, a method of fabricating the TFT, an OLED display device having the TFT, and a method of fabricating the OLED display device.
2. Description of the Related Art
In general, a polycrystalline silicon (poly-Si) layer is widely used as a semiconductor layer for a thin film transistor (TFT) because the poly-Si has a high field-effect mobility, can be applied to a high-speed operating circuit, and can used to configure a complementary-metal-oxide-semiconductor (CMOS) circuit. A TFT using a poly-Si layer may be typically used as an active device of an active-matrix liquid crystal display (AMLCD) or a switching device or a driving device of an organic light emitting diode (OLED) display device.
Methods of crystallizing an a-Si layer into a poly-Si layer may include a solid phase crystallization (SPC) method, an excimer laser crystallization (ELC) method, a metal induced crystallization (MIC) method, and a metal induced lateral crystallization (MILC) method. Recently, a vast amount of research has been conducted on methods of crystallizing an a-Si layer using a crystallization-inducing metal, because these methods allow for a-Si layer to be crystallized at a lower temperature for a shorter amount of time than does an SPC method.
Typical methods of crystallizing an a-Si layer using a crystallization-inducing metal are a MIC method and a MILC method. In these methods, however, the device characteristics of a TFT may be degraded due to contamination caused by the crystallization-inducing metal.
In order to prevent the contamination caused by the crystallization-inducing metal, a gettering process may be performed after an a-Si layer is crystallized using the crystallization-inducing metal to remove the remaining crystallization-inducing metal. Conventionally, the gettering process is performed using impurities, such as phosphorus (P) gas or noble gas, or by forming an a-Si layer on a poly-Si layer. However, in the conventional methods, the crystallization-inducing metal may not be effectively removed from the poly-Si layer, so a leakage current may still be problem.